01-15-2024, 05:40 PM | #1 |
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CEL Throwing Mixture too Lean
Car was in for service today. 2019 330xi which has 42K miles. Had engine oil, tire rotation, inspection, alignment, brake fluid done. As I'm pulling into my garage right after the service appt, CEL lights up. I pull the codes and it says mixture too lean on ECU #1.
One thing I noticed over the past few weeks is my fuel efficiency, according to the car, has gone down significantly. I usually get 25-30mpg driving around town and it's dropped to around 17mpg. It's not rough at idle and accelerating fine. Anybody seen this before? The joys of German car ownership.... |
01-16-2024, 06:09 AM | #2 |
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Most likely one of the lambda sensors in the exhaust system is faulty. There are two (before and after catalytic converter) It measures the oxygen in the exhaust gases and adjusts the fuel/air mixture to ensure the engine is running optimally. If it goes wrong it can cause rough running, excessive emmisions and poor fuel consumption. Get the codes read to confirm. If it's that, its and easy fix, screw out, screw in replacement part.
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01-16-2024, 08:26 AM | #3 | |
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01-16-2024, 01:35 PM | #4 | |
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01-19-2024, 04:59 AM | #5 | |
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01-19-2024, 06:11 PM | #6 |
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Shop replaced the fuel vapor solenoid, gave the car back. I drove it home and the CEL is back on again. Any ideas, guys? Can someone walk me through diagnosing the MAF and O2 sensors?
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01-19-2024, 09:45 PM | #7 |
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First check should be visual inspection of vacuum lines. Sometimes a small hose falls off the fitting, or on older cars the hose deteriorates and develops a leak.
I’ve never replaced the MAF sensor on my BMW, but on most cars you can unplug and remove the MAF sensor, use MAF cleaner on it, and reinstall. If O2 sensors are bad I think the only choice is to replace them. When sensing O2 they make very small voltage changes that are fed back to the computer, and I think you would need special test equipment to know if they were working properly. |
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01-20-2024, 02:52 AM | #8 |
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[QUOTE=Bc2005;30829158]First check should be visual inspection of vacuum lines. Sometimes a small hose falls off the fitting, or on older cars the hose deteriorates and develops a leak.
I’ve never replaced the MAF sensor on my BMW, but on most cars you can unplug and remove the MAF sensor, use MAF cleaner on it, and reinstall. If O2 sensors are bad I think the only choice is to replace them. When sensing O2 they make very small voltage changes that are fed back to the computer, and I think you would need special test equipment to know if they were working properly. Thank you! I was also thinking clean the MAF. Going to try that today. |
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01-20-2024, 10:23 AM | #9 |
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I removed and cleaned the MAF this morning. Drove it around for about 20 minutes and no CEL so far. Not declaring victory yet. I want to drive it a bit more.
I've been using my scan tool to monitor the fuel trim data. I don't 100% understand it yet. At first, it looked out of spec for the MAF. After cleaning, it looks better. Car is showing a pending lean code but it hasn't thrown a CEL yet. Not sure what to think. I'm going to drive it more today and see what happens. |
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02-12-2024, 11:53 AM | #10 | |
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02-12-2024, 03:10 PM | #11 | |
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